Why drive fuel pump from ECU ?

[steve-V8s]

Other than where the ECU acts as part of the immobiliser circuit what is the benefit of driving the Fuel pump relay from the ECU rather than from a ignition switched feed ?

[annodomini2]

Its a failure mode, the ignition system will also be powered from the ECU, so if the key is removed while you're doing 60 down the motorway you don't lose the engine.

[Steve_D]

It is primarily a safety feature as the ECU will switch off the fuel pump if it detects that the engine is not running. So in the event of a crash and where the engine stops it does not continue to pump fuel.

When you start the engine most ECU give a prime pulse of about 2 seconds when the ignition is turned on and does not turn the pump on again until the engine is cranking.

Steve

Edited by Steve_D on Sunday 22 March 14:58

[eliot]

Steve_D said:

It is primarily a safety feature as the ECU will switch of the fuel pump if it detects that the engine is not running. So in the event of a crash and where the engine stops it does not continue to pump fuel.

When you start the engine most ECU give a prime pulse of about 2 seconds when the ignition is turned on and does not turn the pump on again until the engine is cranking.

Steve

Indeed.

[anonymous-user]

Also of course, these days, most PI gasoline fuel systems are "returnless", i.e. they do not use a mechanical pressure regulator, but PWM the fuel pump to generate only the fuel flow they require (which of course varies with engine rpm and load) in order to do this, the fuel pump must be controlled by the engine ecu.